1. Field of the Invention
This invention relates to a picture image forming apparatus suitable for use in a heat transfer printing type color copying machine or the like, and more particularly, a picture image forming apparatus wherein read means of a manuscript and picture image forming means are driven by independent clock pulses.
2. Description of the Prior Art
In recent years, a heat transfer type color copying machine has been proposed in which a multicolor heat transfer ink ribbon, for example, is used for effecting color copying. Briefly stated, according to this copying machine, a manuscript is read by scanning it with optical read means, that is scanning means for deriving out picture image informations (color signals of light), converting the picture image informations into color signals corresponding to respective colors of ink of the heat transfer printing ink ribbon, selecting corresponding ink portions of the heat transfer printing ink ribbon in accordance with the color signals, and then heat transferring the ink onto a copying paper by using a heat sensitive head so as to transfer print respective colors onto the copying paper, thus effecting color copying.
The prior art copying machine of the type described above is constructed such that a series of operations starting from the reading of the manuscript with the scanning means to the transfer printing of the picture image with the thermal head are performed with a fixed clock pulse. However, the read speed of a photoelectric converter utilized for reading the manuscript with the scanning means, the transfer printing speed (that is the picture image forming speed) determined by the capacity of a power source and the heat storage of the thermal head, and the processing speed of signal converting means that effects color conversion are not equal so that when one tries to drive these means with a definite clock pulse it is difficult to optimumly design various elements, thereby resulting in faults and cost up.
Also in the prior art copying machine, at the time of reading the manuscript, the photoelectric converting apparatus is moved along the manuscript, while at the time of transfer printing the picture image the copying paper is moved to a point in front of the thermal head, and pulse motors are used for moving the photoelectric converting apparatus and the paper at high accuracies. When it is intended to operate the pulse motors at high speeds higher than the self-starting regions, it is necessary to slowly increasing and decreasing their speeds. In such case, it is impossible to drive the pulse motors with a clock pulse of a fixed frequency.